Magnet Glossary

Definitions of the most common magnet technical terminology

• Air Gap

  Air gap is the "external" distance from one pole of the magnet to the other though a non-magnetic material (usually air).

• Anisotropic

  An anisotropic material has different properties in different directions. For example, wood with a grain is stronger in one direction than another. Like wood, neodymium magnets are also anisotropic. Even before it is magnetized, a neodymium magnet has a "preferred" magnetization direction. Learn About Magnetization Direction

  Neodymium magnets are made with a preferred magnetization direction which cannot be changed. These materials are either manufactured in the influence of strong magnetic fields or pressed a specific way, and can only be magnetized through the preferred axis. Sintered Neodymium (Iron Boron) and Samarium Cobalt magnets are anisotropic.

• B/H Curve

  The BH curve is the result of plotting the value of the magnetic field (H) that is applied against the resultant flux density (B) achieved. The BH curve describes the qualities of any magnetic material. Graphical explanation of B/H curve.

• BH_max (Maximum Energy Product)

  BH max is the Maximum Energy Product at the point on the B/H Curve that has the most strength, expressed in MGOe (MegaGaussOersteds). When describing the grade of a neodymium magnet, this number is commonly referred to as the "N" number, as in Grade N52 magnets.

  BH max is the area inside the red box, under the curve in the picture.

  

• Br_max (Residual Induction)

  Br max is also called "Residual Flux Density" and is when the magnetic induction remaining in a saturated magnetic material after the magnetizing field has been removed. This is the point at which the hysteresis loop crosses the B axis at zero magnetizing force, and represents the maximum flux output from the given magnet material. By definition, this point occurs at zero air gap, and therefore cannot be seen in practical use of magnet materials.

  

• C.G.S.

  C.G.S. is the abbreviation for the "Centimeter, Grams, Second" system of measurement.

• Coercive Force (Hc)

  Coercive force is the demagnetizing force necessary to reduce observed induction B to zero after the magnet has previously been brought to saturation and is measured in Oersteds.

  

• Curie Temperature (T_c)

  Curie temperature is the temperature at which a magnet loses all of its magnetic properties.

• Demagnetization Curve

  The demagnetization curve is the second quadrant of the hysteresis loop and generally describes the behavior of magnetic characteristics in actual use. It is also known as the B-H Curve. Find these curves for some of our most popular magnet grades on our BH Curves page.

• Demagnetization Force

  Demagnetization force is a magnetizing force, typically in the direction opposite to the force used to magnetize it in the first place. Shock, vibration and temperature can also be demagnetizing forces.

• Dimensions

  Dimensions are the physical size of a magnet including any plating or coating.

• Dimensional Tolerance

  Dimensional tolerance is an allowance, given as a permissible range, in the nominal dimensions of a finished magnet. The purpose of a tolerance is to specify the allowed leeway for variations in manufacturing.

• (Magnetic) Dipole Moment (m)

  A magnetic dipole moment is a quantity that describes the torque a given magnet will experience in an external magnetic field.

  Some folks (like physicists) use a magnetic dipole model to simulate or mathematically model a magnet or group of magnets. Mathematically, it's easier than considering the complexities of weird magnet shapes. It's not theoretically perfect. Using it won't always match measured field strengths near a neodymium magnet. It works great for a sphere, but isn't correct near other shapes like discs or blocks. It's a great approximation when you're measuring far away from a magnet, but not so good close up, especially near the edges of a magnet.

  Calculate the dipole moment using the formula m = dipole moment in A m² = Br x V / μ_o, where:

  • Br is Br max, the Residual Flux Density, expressed in Tesla.
  • V is the volume of the magnet, expressed in cubic meters.
  • μ_o is the permeability of a vacuum, or 4 π x 10^-7 N/A².

• Electromagnet

  An electromagnet is a magnet consisting of a solenoid with an iron core, which has a magnetic field only during the time of current flow through the solenoid. Learn more in our Electromagnets article.

• Ferromagnetic Material

  A ferromagnetic material is a material that either is a source of magnetic flux or a conductor of magnetic flux. Most ferromagnetic materials have some component of iron, nickel, or cobalt.

• Gauss

  Gauss is a unit of magnetic induction (B) and is the number of lines of magnetic flux per square centimeter in the C.G.S. system of measurement. Gauss is equivalent to lines per square inch in the English system, and webers per square meter or tesla in the S.I. system. 10,000 gauss equals 1 tesla.

• Gauss meter

  A gauss meter is an instrument used to measure the instantaneous value of magnetic induction (B) and is usually measured in Gauss (C.G.S.). Also called a DC magnetometer.

• Gilbert

  A Gilbert is the unit of magnetomotive force, F, in the C.G.S. system.

• Hysteresis Loop

  A hyteresis loop is a plot of magnetizing force versus resultant magnetization (also called a B/H curve) of the material as it is successively magnetized to saturation, demagnetized, magnetized in the opposite direction and finally remagnetized. With continued recycles, this plot will be a closed loop which completely describes the characteristics of the magnetic material. The size and shape of this "loop" is important for both hard and soft materials.

  With soft materials, which are generally used in alternating circuits, the area inside this "loop" should be as thin as possible (it is a measure of energy loss). However, with hard materials, the "fatter" the loop, the stronger the magnet will be.

  The first quadrant of the loop (that is +X and +Y) is called the magnetization curve. It is of interest because it shows how much magnetizing force must be applied to saturate a magnet. The second quadrant (-X and +Y) is called the Demagnetization Curve. Graphical explanation of BH curve.

• Induction, (B)

  Induction is the magnetic flux per unit area of a section normal to the direction of flux. Measured in Gauss, in the C.G.S. system of units.

• Intrinsic Coercive Force (H_ci)

  Intrinsic coercive force indicates a material's resistance to demagnetization. It is equal to the demagnetizing force which reduces the intrinsic induction (Bi) in the material to zero after magnetizing to saturation and is measured in oersteds.

• Irreversible Losses

  Irreversible loss is the partial demagnetization of the magnet, caused by exposure to high or low temperatures, external fields, shock, vibration, or other factors. These losses are only recoverable by remagnetization. Magnets can be stabilized against irreversible losses by partial demagnetization induced by temperature cycles or by external magnetic fields.

• Isotropic Material

  Isotropic material is a material that can be magnetized along any axis or direction (a magnetically unoriented material). The opposite of an Anisotropic Magnet.

• Keeper

  A keeper is a soft iron piece temporarily added between the poles of a magnetic circuit to protect it from demagnetizing influences. Also called a shunt. Keepers are generally not needed for Neodymium and other modern magnets. They are more commonly used with older Alnico Horseshoe Magnets.

• Kilogauss

  One Kilogauss = 1,000 Gauss = Maxwells per square centimeter.

• Magnet

  A magnet is an object made of certain materials which create a magnetic field. Every magnet has at least one north pole and one south pole. By convention, we say that the magnetic field lines leave the North end of a magnet and enter the South end of a magnet. This is an example of a magnetic dipole ("di" means two, thus two poles).

  If you take a bar magnet and break it into two pieces, each piece will again have a North pole and a South pole. If you take one of those pieces and break it into two, each of the smaller pieces will have a North pole and a South pole. No matter how small the pieces of the magnet become, each piece will have a North pole and a South pole. It has not been shown to be possible to end up with a single North pole or a single South pole which is a monopole ("mono" means one or single, thus one pole).

• Magnetic Circuit

  A magnetic circuit, consists of all elements, including air gaps and non-magnetic materials that the magnetic flux from a magnet travels on, starting from the north pole of the magnet to the south pole.

• Magnetic Field (B)

  A magnetic field when specified on our site is the surface field or magnetic field refers to the strength in Gauss.

  For axially magnetized discs and cylinders, it is specified on the surface of the magnet, along the center axis of magnetization.

  For blocks, it is specified on the surface of the magnet, also along the center axis of magnetization.

  For rings, you may see two values. B_y,center specifies the vertical component of the magnetic field in the air at the center of the ring. B_y,ring specifies the vertical component of the magnetic field on the surface of the magnet, mid-way between the inner and outer diameters. Magnetic field depictions.

  

• Magnetic Field Strength (H)

  The magnetizing or demagnetizing force, is the measure of the vector magnetic quantity that determines the ability of an electric current, or a magnetic body, to induce a magnetic field at a given point; measured in Oersteds.

• Magnetic Flux

  Magnetic flux is a contrived but measurable concept that has evolved in an attempt to describe the "flow" of a magnetic field. When the magnetic induction (B) is uniformly distributed and is normal to the area (A) the flux, Φ = BA.

• Magnetic Flux Density

  Magnetic flux density is the lines of flux per unit area, usually measured in Gauss (C.G.S.). One line of flux per square centimeter is one Maxwell.

• Magnetic Induction (B)

  Magnetic induction is the magnetic field induced by a field strength (H) at a given point. It is the vector sum, at each point within the substance, of the magnetic field strength and the resultant intrinsic induction. Magnetic induction is the flux per unit area normal to the direction of the magnetic path.

• Magnetic Line of Force

  Magnetic force lines are imaginary lines in a magnetic field that have the direction of the magnetic flux at every point.

• Magnetic Pole

  Magnetic poles are an area where the lines of flux are concentrated.

• Magnetomotive Force (F or mmf)

  Magnetomotive force is the magnetic potential difference between any two points, tends to produce a magnetic field and is analogous to voltage in electrical circuits. It is commonly produced by a current flowing through a coil of wire and measured in Gilberts (C.G.S.) or Ampere Turns (S.I.).

• Material Grade

  Neodymium (NdFeB) magnets are graded by the magnetic material from which they are manufactured. Generally speaking, the higher the grade of material, the stronger the magnet. We find that the Pull Force of a magnet relates directly to the "N" number. Neodymium magnets currently range in grade from N35 to N52. The theoretical limit for Neodymium magnets is grade N64, though it isn't currently feasible to manufacture magnets this strong. The grade of most of our stock magnets is N42 because we feel that N42 provides the optimal balance between strength and cost. We also stock a wide range of sizes in grade N52 for customers who need the strongest permanent magnets available.

• Maximum Energy Product (BH_max)

  Maximum energy product is the magnetic field strength at the point of maximum energy product of a magnetic material. The field strength of fully saturated magnetic material measured in Mega Gauss Oersteds, MGOe.

• Maximum Operating Temperature (T_max)

  Maximum operating temperature, also known as maximum service temperature, is the temperature at which the magnet may be exposed to continuously with no significant long-range instability or structural changes.

• Maxwell

  A maxwell is a unit of magnetic flux in the C.G.S. electromagnetic system. One maxwell is one line of magnetic flux.

• Magnetization Curve

  The magnetization curve is the first quadrant portion of the hysteresis loop (B/H) curve for a magnetic material.

• Magnetizing Force (H)

  Magnetizing force is the magnetomotive force per unit of magnet length, measured in Oersteds (C.G.S.) or ampere-turns per meter (S.I). and is the C.G.S. unit for total magnetic flux, measured in flux lines per square centimeter.

• MGOe

  MGOe stands for mega (million) Gauss Oersteds and is the unit of measure typically used in stating the maximum energy product for a given material. See Maximum Energy Product.

• North Pole

  The north pole of a magnet is the one attracted to the magnetic north pole of the earth. This north-seeking pole is identified by the letter N. By accepted convention, the lines of flux travel from the north pole to the south pole.

• Oersted (Oe)

  An Oersted is the C.G.S. unit for magnetizing force. The English system equivalent is Ampere Turns per Inch (1 Oersted equals 79.58 A/m). The S.I. unit is Ampere Turns per Meter.

• Orientation

  Orientation is used to describe the direction of magnetization of a material.

• Orientation Direction

  Orientation direction is the direction in which an anisotropic magnet should be magnetized in order to achieve optimum magnetic properties.

• Paramagnetic Materials

  Paramagnetic materials are materials that are not attracted to magnetic fields (wood, plastic, aluminum, etc.) and have a permeability slightly greater than 1.

• Permanent Magnet

  A permanent magnet is a magnet that retains its magnetism after it is removed from a magnetic field. A permanent magnet is "always on". Neodymium magnets are permanent magnets.

• Permeance (P)

  Permeance is a measure of relative ease with which flux passes through a given material or space. It is calculated by dividing magnetic flux by magnetomotive force. Permeance is the reciprocal of reluctance.

• Permeance Coefficient (P_c)

  The permeance coefficient ia also called the load-line, B/H or "operating slope" of a magnet and is the line on the Demagnetization Curve where a given magnet operates. The value depends on both the shape of the magnet and its surrounding environment (some would say, how it's used in a circuit). In practical terms, it's a number that defines how hard it is for the field lines to go from the north pole to the south pole of a magnet. A tall cylindrical magnet will have a high Pc, while a short, thin disc will have a low Pc.

  Our online Pull Force Calculator can calculate Pc for common shapes. It assumes a single magnet in free space. Other nearby magnets or ferromagnetic materials can change matters.

• Permeability (μ)

  Permeability is the ratio of the magnetic induction of a material to the magnetizing force producing it (B/H). It is a measure of how much a material becomes magnetized in the presence of a magnetic field.

  The magnetic permeability of a vacuum (µ_o) is 4π×10^-7 N/A².

• Plating/Coating

  Most neodymium magnets are plated or coated in order to protect the magnet material from corrosion. Neodymium magnets are mostly composed of neodymium, iron, and boron. The iron in the magnet will rust if it is not sealed from the environment by some sort of plating or coating. Most of the neodymium magnets that we stock are triple plated in nickel-copper-nickel, but some are plated in gold, silver, or black nickel, while others are coated in epoxy, plastic or rubber.

• Polarity

  Polarity is the characteristic of a particular pole at a particular location of a permanent magnet and differentiates the North from the South Pole.

• Pole

  A pole is an area where lines of magnetic flux are concentrated.

• Pull Force

  Pull force is the force required to pull a magnet free from a flat steel plate using force perpendicular to the surface, or the limit of the holding power of a magnet. The pull force listed is actual data acquired by testing using our state-of-the-art force test stand. A comprehensive table of the pull force for all of our stock magnets is available here: Pull Force Table

  We test for two different values of pull force using two different setups. Read more about these two pull forces here: Pull force explanation.

• Rare Earth

  Rare earth is commonly used to describe high energy magnet material such as NdFeB (Neodymium-Iron-Boron) and SmCo (Samarium-Cobalt).

• Relative Permeability

  Relative permeability is the ratio of permeability of a material to that of a vacuum. In the C.G.S. system, the permeability is equal to 1 in a vacuum by definition. The permeability of air is also for all practical purposes equal to 1 in the C.G.S. system.

• Reluctance (R)-

  Reluctance is a measure of the relative resistance of a material to the passage of flux. It is calculated by dividing magnetomotive force by magnetic flux. Reluctance is the reciprocal of permeance.

• Remanence, (B_d)

  Remanence is the magnetic induction that remains in a magnetic circuit after the removal of an applied magnetizing force.

• Residual Flux Density (Br_max)

  See Br_max.

• Residual Induction (Br_max)

  See Br_max.

• Return Path

  A return path is a conduction element in a magnetic circuit which provides a low reluctance path for the magnetic flux.

• Reversible Temperature Coefficient

  Reversible temperature coefficient is a measure of the reversible changes in flux caused by temperature variations.

• Saturation

  Saturation is the state where an increase in magnetizing force produces no further increase in magnetic induction in a magnetic material.

• Shunt

  A shunt is a soft iron piece temporarily added between the poles of a magnetic circuit to protect it from demagnetizing influences and is also called a keeper. Not needed for Neodymium and other modern magnets.

• S.I.

  S.I. is the abbreviation for "Système International". It refers to the International Standard System of units and is also known as the MKS system.

• South Pole

  The south pole of a magnet is the one attracted to the south pole of the earth. This south-seeking pole is identified by the letter S. By accepted convention, the lines of flux travel from the north pole to the south pole.

• Stabilization

  Stabilization is the process of exposing a magnet or a magnetic assembly to elevated temperatures or external magnetic fields to demagnetize it to a predetermined level. Once done, the magnet will suffer no future degradation when exposed to that level of demagnetizing influence.

• Surface Field (Surface Gauss)

  Surface field is the magnetic field strength at the surface of the magnet as measured by a Gauss meter. Our Surface Field Table is a comprehensive table of the surface field for all of our stock magnets.

• Temperature Coefficient

  Temperature coefficient is a factor that is used to calculate the decrease in magnetic flux corresponding to an increase in operating temperature. The loss in magnetic flux is recovered when the operating temperature is decreased.

• Tesla

  Tesla is the S.I. unit for magnetic induction (flux density). One Tesla equals 10,000 Gauss.

• Weber

  A weber is the S.I. unit for total magnetic flux; the practical unit of magnetic flux. It is the amount of magnetic flux which, when linked at a uniform rate with a single-turn electric circuit during an interval of 1 second, will induce in this circuit an electromotive force of 1 volt.

• Weight

  The weight of a single magnet.